Loops in C

1. Loops in C ATS 315

2. Loops • Are used to perform some action multiple times. • Are crucial to most C programs that are useful.

3. Two Main Kinds of Loops • Loops that run a specific number of times. • “for” loops • Loops that run a flexible number of times, if at all. • “while” loops

4. “for” loops • Require a “counter” that keeps track of how many times the loop has run. • Typically this is an integer, but it doesn’t have to be.

5. “for” loop syntax • Sample loop that will run 5 times. main () { int i; for(i=0;i<5;i++) { printf (“%d\n”,i); } }

6. “for” loop syntax • On the first pass through the loop, i=0. main () { int i; for(i=0;i<5;i++) { printf (“%d\n”,i); } }

7. “for” loop syntax • “What the loop does” is inside a set of curly braces. main () { int i; for(i=0;i<5;i++) { printf (“%d\n”,i); } }

8. “for” loop syntax • Traditionally we indent the stuff inside a loop a little farther. main () { int i; for(i=0;i<5;i++) { printf (“%d\n”,i); } }

9. “for” loop syntax • After each pass through the loop, the “loop control variable” will be changed as shown here. main () { int i; for(i=0;i<5;i++) { printf (“%d\n”,i); } }

10. “i++” ?!?!?!?!!!!??? • i++ is a shortcut for “i=i+1” • To increase in a different “step”, just be more explicit about it: • i=i+2

11. “for” loop syntax • As long as the loop control variable passes the “condition”, it will continue to loop. main () { int i; for(i=0;i<5;i++) { printf (“%d\n”,i); } }

12. “for” loop syntax • This loop will run 5 times: • i=0,1,2,3,4 main () { int i; for(i=0;i<5;i++) { printf (“%d\n”,i); } }

13. “for” loop syntax • Traditional format: • There are three “arguments” in the for loop: • for(i=0;i<n;i++) { • }

14. “for” loop syntax • Traditional format: • 1. The starting value of the loop—usually zero. • for(i=0;i<n;i++) { • }

15. “for” loop syntax • Traditional format: • 2. The “condition” for the loop—it will run as long as this is true. • for(i=0;i<n;i++) { • }

16. “for” loop syntax • Traditional format: • 3. The “increment” of the loop—how to modify the value of the loop control variable. • for(i=0;i<n;i++) { • }

17. Floating Point Loops • for(pressure=1000.0;pressure<1024.0; pressure=pressure+4.0) { • }

18. Nested Loops • One thing that could be inside of a loop is another loop. • Excellent for working with grids of data…

19. for(i=0;i<5;i++) { for(j=0;j<3;j++) { printf (“%d %d\n”,i,j); } } 0 0 0 1 0 2 1 0 1 1 1 2 2 0 2 1 2 2 3 0 3 1 3 2 4 0 4 1 4 2 Nested Loops

20. The “while” Loop • Is used when you don’t know in advance how many times the loop should run… it just needs to run “while” something is true.

21. “while” loop syntax • Loop control variable needs to be “initialized”. tempF = 0.; while (tempF > -98.0) { printf (“Enter a temp in F to convert to C.\n”); printf (“Or enter -99 to end.\n”); scanf(“%f”,&tempF); tempC = (tempF-32.)*(5./9.); printf (“The temperature is %4.1fC.\n\n”); }

22. “while” loop syntax • Loop will repeat “while” condition is true. tempF = 0.; while (tempF > -98.0) { printf (“Enter a temp in F to convert to C.\n”); printf (“Or enter -99 to end.\n”); scanf(“%f”,&tempF); tempC = (tempF-32.)*(5./9.); printf (“The temperature is %4.1fC.\n\n”); }

23. “while” loop syntax • Loops are generally indented. tempF = 0.; while (tempF > -98.0) { printf (“Enter a temp in F to convert to C.\n”); printf (“Or enter -99 to end.\n”); scanf(“%f”,&tempF); tempC = (tempF-32.)*(5./9.); printf (“The temperature is %4.1fC.\n\n”); }

24. Uses of “while” • “while” loops are generally used to trap errors.

25. Your Assignment • Make a table of wind chill temperatures! • Prompt the user for an air temperature • Prompt the user for a lowest wind speed • Prompt the user for a highest wind speed • Prompt the user for an interval